In a system of multiple parallel generators, each generator has its own generator paralleling breaker which is used to connect it to a common bus so that it can provide power to the electrical load. When there is no power on the bus, only generator is allowed to close its breaker to connect to the bus. Once that generator has closed its breaker, the bus becomes live and the remaining generators typically synchronize output voltage, frequency, and phase to match that of the bus before closing each respective breaker.
The automatic closing of a generator paralleling breaker to a dead bus requires the control system to know that the bus lacks power. One approach is to determine if there is voltage on the bus. If there is no voltage, the bus is dead.
However, the bus will appear to be dead if the voltage sensing circuit is open or shorted. Should the control system sense the bus as being dead, but in actuality it is live, closing the generator breaker to the bus without synchronizing the output voltage, frequency, and phase may result in generator damage. This damage may include failed generator rotating rectifiers or failed surge suppressors. At a minimum, closing a generator to a bus without synchronization will stress the generator and may shorten generator life.
With current designs, incorrect sensing of a dead bus has various sources. Incorrect sensing of a dead bus can be caused by wiring connections which have not been made, are broken, or were disconnected inadvertently or intentionally during servicing or testing procedures. Incorrect sensing can also be caused by open fuses in the bus voltage sensing circuit, or a disconnected bus sensing transformer. One of the most common causes of failure of bus voltage sensing is human error during commissioning or servicing of the generator system.
Thus, there is an ongoing need for further contributions in this area of technology. The various embodiments of the present application provide such contributions.